Flight computing system



Nov. 4, 1958 Filed June -14, 1954 R. G. lSTERN ETAL FLIGHT COMPUTING SYSTEM 3 sheets-sheen; 1

coE'FF mem' 0F HFT INVENTORS ROBERT G. STERN LL ALBERT. SHERMAN Mmmm/Ex Nov. 4, 195s R. G. STERN HAL 2,858,623

FLIGHT COMPUTING SYSTEM Filed June 14. 1954 3 Sheets-Sheet 2 CONTROL msTxzuc-roks Flc-1.12

INVENTORS ROBERT G STERN ALBERT J. SHERMAN Jn A Tram/Ex Nov. 4, 1958 R. G. STERN ETAL 4 FLIGHT COMPUTING SYSTEM 3 Sheets-Sheet 3 Filed June 14, 19,54

INVENTORS' ROBE RT Cv ALERT J.. SHERMAN Jouhzou mu- 02;) f 9.953,52..

STERN MATTO/THEY United States Patent 2,858,623 FLIGHT COMPUTING SYSTEM .Robert G. Stern, West Caldwell, N. J., andAlbert J. Sherman, New York, N. Y., assignors to Curtiss-Wrigh Corporation, a corporation of DelawareV f Application June 14, 1954, Serial No. 436,532 Z Claims. (Cl. 35-12) yv Y.

This invention relates to ight trainers and more parl projected wing area. The formula lumps together items;

of parasitic and induced drag to approximate the total drag on the aircraft which is simulated by the trainer.: Whereas various methods have been used heretofore in determining total drag, it is preferable for the purpose of more accurately determining drag, 4to compute induced drag separately. It is especially important -in4 accurately determining drag for large angles of attack and low speeds that the induced drag be separately computed. In addition to computing induced drag separately, it is desirable f, to compute separate items of parasiticdrag such asassociated with angle of attack, v'side-slip, wing ice, 4rudder v angle and wing liap position in order to more accurately determine the total drag. f It is an object of this invention to provide in trainer apparatus for computing ight conditions, novel and im- 'j proved means for more accurately determining drag than l heretofore, wherein items of induced and parasitic ldrag are separately computed. y It is another object of this inventionto provideA in t trainer apparatus for computing ight conditions, novel f and `improved drag computing means of thel described @type wherein induced drag is computed by suitable appar {ratus as a function of normal acceleration and'coeliicient of lift. t

It is still another object of this invention to provide a novel and improved liight training apparatus which is' particularly adapted to provide for the accuratedete'rmination of air speed.

The invention will be more fully set forth in the following description referring to the accompanying drawings, and the features of novelty will be pointedvout with 'parl ticularity in the claims annexed to and forming a partof this specification. p'

Referring to the drawings Fig. 1 is a schematic illustration showing ight training apparatus which incorporates the features of this invention; Figs. 2,' 3 and- 4 show additional control circuitrytying in with various components of the ight training apparatus of Fig. l'.

2,858,623 Iatented Nov.. 4, 1858 of other servo systems shown in the drawings. Referring to v'the true air speed servo (Vt) as an example of the various servo systems, such servo includes a servo arnplilier 2 to which are applied a number of controlled voltages hereinafter considered in detai1,a motor 3 rey sponsive to the amplifier output, a'feed-back generator 4 tude of the control voltage.

driven by the motor 3, and a number of potentiometers as for example 5, 6 and 7 having, their slider contacts connected through a gear reduction lbox 8 to the motor generator combination. Servo amplifier 2 is a summing amplifier for determining the resultant of the input volt ages and is of a type well-known in the art for algebraically summing a plurality of A. C. voltages of varying magnitude and polarity. A detailed circuit illustration of the servo amplifier is therefore unnecessary.

The servomotor 3 is of the two-phased type, having a control phase 9 which is energized by the amplifier output, and another phase 10 which is energized by a constant reference A. C. voltage e1 dephased 90 from the control voltage. The operation of this type of motor is well-known, rotation being in one direction when the control and reference voltages of the respective phases have the same instantaneous polarity, and in the opposite direction when the instantaneous polarity of the control voltage is reversed with respect to the reference voltage, the rate of rotation in both cases depending on the magni- The generator 4 which is driven by the servomotor is a two-phased generator having one phase 11 energized by a 90 de-phased A. C. reference voltage e2, the other phase 12 generating according to the motor speed a feed-back voltage en, for purposes of velocity control. v

The potentiometer resistance elements such as S, 6 and 7 of the true air speed servo (Vt) and the other potentiometers shown in the drawings may be of the wellknown wound card type and are of circular band form in practice, but are diagrammatically illustrated in plane Referring to Fig. 1, the flight training apparatus inand induced). This servo is typical development for clarity. A structural arrangement that may be conveniently used for a servomotor and potentiometer combination of the character above referred to is shown in Patent Number 2,341,749 issued December 2, 1947 to R. B. Grant for Potentiometer Housing and Positioning Structure.

, Potentiometer cards 5, 6 and 7 are provided with slider contacts such as 13, 14k and 15 respectively which are positioned along the respective cards by the servomotor which connects with the slider contact through the gear reduction box 8 and suitable mechanical connections 16. The slider contacts derive, i. e. pick oli potentiometer voltages depending on the respective contact position. Each potentiometer for the various servos shown in the drawings is shaped or contoured, and designed with suitable shunting resistances where required so that the derived voltages at the potentiometer contacts bear a certain relationship to linear movement of the slider contacts depending upon the particular function of the potentiometer, and has a voltage impressed across its terminals depending as to instantaneous polarity and magnitude also upon the function of the potentiometer. t

In accordance with our invention the true airspeed servo (Vt) computes true air speed according to the magnitude of control voltages representing the effects of thrust, gravity, parasitic drag, and induced drag on the speed of the aircraft for any ight attitude. As indicated in the drawing the various input signals to the ampliier 2 of the true air speed servo (Vt) are gaseosa The input signal Dp Dt -lm and m respectively yrepresent the effect ofparasitic and induced; drag` which tend to decrease air speed. All of the various input signals `have been reversed insign, i. e. those items tending to increase air speed Aare represented by a signal having a negativesign :and thoseoitems tending to decrease air speed are represented by signals, which are prefaced by a positive sign. Sin'ce all the signs of,t he various input signals are reversed with respectto the physical state of affairs the `servo maynevertheless be operated to compute true .air speed, rotation being yin, one direction as air lspeed increases and in the opposite direction as air Aspeed decreases. Actually Lthe inputwsignals to servo amplifier 2 represent in summation-acceleration of the aircraft and such input quantities areA integrated in the servo so that theservo position at any particular time corresponds to the true air speed of the' aircraft.

The input signal as the present invention.,V The amplifier is connected't'o' the primary 18 of a'transformer 19 which hasthe negative output terminal of its secondary'Zilconnectedpver line 21 to the slider contact 22 of load potentiometer 23. The potentiometer 23 as shfown connects aty onelend through a resistor 2'4 to groundpandlat thel Sametime connects over line 25 with the true air speedservoarnplifier 2. Potentiometer.'23is a dividing potentiometer having an output which lis determined' according' to'the voltage at slider contact22 and accordirigjto the position of the slider contact.v The voltagelat'slider"contact'22 which connects kover `line '2l with theft'ran'sformer'secondary 20 at its negative output 'terminal is thevoltage output at ysuch terminal, -fTrepresenting't l I position of the slider contact 22 ofn'potentiometericai'd-Z is determined by the setting of dial18,' vvhich"connects with the slider contact kby means of suitable'frme I connections 26. Thel dialis positioinedfbyin instructor according to a supposed loadedyveg'ht fortheaireraft, the dial being so calibrated thatthe VouI lut* .,v ltageV of potentiometer 23 appearing in line 25' provides? an 'input signal l to amplifier 2 representing as a negative quantity the thrust divided by the mass of the aircraft. The instructors dial 18 which has been referred to also controls the position of slider contacts 27 and 2S of ther'lod'pbtentiometers 29 and 30 respectivelywhich are used for purposes hereinafter set forth. 'A position for the slider con- 4 At a t:t,svu22,n 2 7 and 28 at the lower end of each of cards 23, 29 and 30 respectively corresponds to a lightly loaded condition of the aircraft, whereas a position for the slider contacts farther up the cards corresponds to a greater degree of loading.

Considering now the input signals -l-g sin 0 and -g sin a to servo amplifier 2 representing the effect of gravity on air speed, Where g is acceleration due to gravity, 6 is the angle of pitch, vand a is the angle of attack; such input s igalse deteinined in accordance with the operation of a pitch servov `(0) designated by thepreference character 31, and angle of` attack servo (a) bearing the reference character 32. Operation of the pitch servo (e) is in turn dependent uponthe operation of a rate of pitch servo (my), and the operation of the angle of attack servo (o) is dependent upon the operation of the rate of pitch servo w'y, tr ue airspeed servo Vt), a (V12) servo, the setting ofthe aircraft loading' dial 1S', "andup'on a control voltage representing ceeiiieient of lift (CL) Therate of pitchservo (wy) which Vi'sindicated b'y ref erenc'efc'haracter 33 is controlled Vin a 'manner 'indicated in QSfPAtet No. 2,687,580, granted on August l3l, 11954 toRiehfa'i'd'Carl Dehiiel, Vand as shown includes 'in-A ptdsigiial ('Mp)"representing`a pitching moment derived ccoidin'g'to' the niovin'ent "of "slidr'c'ontact '34 on 'potentiometer 3S. MPofentio'n'leter''35 'i's"en`e`rgized at opposite ends by A. C. voltages opposite in sign representing indicated velocity square (Vi2),"the voltages being derived from-the V1? servo 45 in a Well-known manner, for example in theA s amernanner `as theivitag'es '-l-VT and -VT are lderivedfromfthe VT servo 1 as hereinafter described. The servo v per sc operates in a manner hereinafter indicated. L' lhe, slider contact'34 is moved along the `poten tiometegS as indicated" in the aforesaid Patent No. 2,687,580 in accordance with the'operation of an elevatorvl.co ritroll.l. `The wy servoV includes a potentiometer' hayingoa slider contact v37"\vhich is moved along 'the potentiometer card according tothe resultant of'the input signals to the wy servo. As 'further Vindicated in Patent No.Y 2,687,580 potentiometerfcard 36 is energized at 'opposite ends by positive and negative reference voltages .-|,E and .'-E respectively and-is grounded at the midpoinLv lSlider contact 3 7 connects over lines '38 and V'39 vvith the servo amplifier 40 of the pitch servo (9),.an'd a voltage derived` at contact 37 determines the input signal wy totheamplier 40 representing lthe rate of change of angleof pitch. The only other signal fed to the'amplier 40 of thepitch servo is a feed-back signal efb generated by the servo generator. Accordingly the pitch servo which is an integrating servo is operated to a position determinat'ive of the pitch angle. Operation of the pitch vse'rvoresults in positioning a Vslider contact 41 Valong potentiometer card`42, the potentiometer` cardbeing energizfed-at opposite sides `bya positive and negative A. C. voltage -i-E and -E respectively, and being grounded at ,itsv mid-point. The potentiometer card` is Wound'cosinusoidavlly to, provide for the derivation of a sine function at contact 41.* As'indicated slider contact41 connects over lines 43 and 44 with the true air `speed servo amplifier providing for the input signal g sini0. As will be apparent from the dravving a position for the pitch servo corresponding toA a position of slider contact'41 at the midpoint of potentiometer card 42 indicates a pitch angle of O, whereas a positionfor lthe pitch servo and corresponding position for slider contact"41 onthe positive s ide of the card indicatesa positive angle of pitch. A position for the pitch servo and corresponding position for` slider contact 141 on the negative side of the potentiometer card-42 indicates aneg'ative'angle of-pitch.

fAs has: previously been indicatedy the input signal J-,g sin .a'gto the rtrue air speed servoamplifier'2` is dependeritupon operationy of' an angle of attack servo (e0- designated` by thereference character. 32 which in 'turn isdependent-.upon theoperation of rateof pitch 'servo'(wy),'t`rueaispeed' servo'Vt, a (VP) servo bearing the reference character 45, they setting of aircraft loading dial 18', and upon a control Avoltage representing coeiii'- cient of lift (CL). Derivation of the coeiicient of lift voltage (CL) as a control factor in the operation of the angle of attack servo (a) will be rst considered, reference being made to Fig. 2 wherein apparatus for deriving such voltage is shown. v

Included in the apparatus for deriving the coeicient of lift voltage CL is transformer 19, the (VP) servo 4S and the (a) servo 32. The transformer 19 is connected at the negative output terminal of the secondary winding 20 over a line 46 with the slider contact 47 of a potentiometer 48 included in the (VF) servo system. Potentiometer 48 is a dividing potentiometer which as shown connects near one end through a resistor 49 with ground. The slider contact 47 is positioned along 4the potentiometer card according to the operation of the (V12) servo to provide an output voltage for the potentiometer 48 determined by the quotient The output voltage of the. potentiometer is fed over line 50 to an amplifier 51 which connects with the primary S2 of transformer 53, transformer 53 providing the voltages -i-TC and -Tc representing thrust coecient at the positive and negative terminals respectively of its secondary winding 54.

The negative output terminal of the secondary winding S4 of transformer 53 connects with potentiometers 55 and 56 of the angle of attack (a) servo. As shown the negative output terminal of the secondary winding 54 connects over lines 57 and 58 with potentiometer 55 at an intermediate point thereof. The negative terminal connects with potentiometer 56 over line 57, a resistor 58 and the l'ine 59 to lone end of the potentiometer and to an intermediate point. As shown, potentiometer 55 connects near one end through a resistor 60 with ground, whereas potentiometer 56 is grounded at an intermediate point and connects through the resistor 61 and over-line 62 with the positive output terminal of secondary winding 54. Potentiometers 55 and 56 include slider contacts 63 and 64 respectively which are moved along the potentiometer cards according to the operation of the angle of attack servo (a), voltages being derived at the slider contacts as a function of the thrust coe'icient Tc and angle of attack a for use in computing components of the coefficient of lift voltage CL. The angle of attack servo (a) includes other potentiometers 65 and 66, the potentiometer65 being connected at one end through a resistor 67 to ground and energized at an intermediate point by the negative A. C. voltage -E. Potentiometer 66 connects t-o ground at an intermediate point and is energized at its one end which connects through resistor 68 with a positive A. C. voltage -l-2E, Whereas the potentiometer is energized at the other end and at an intermediate point according to the output voltage at the slider contact of another potentiometer card 69. As shown potentiometer 69 has its slider contact 70 connected to potentiometer 69 over line 71, resistor 72, and connection 73. The slider contact 70 is moved along the card 69 by means of the instructors wing ice control dial 74 which is connected with contact 70 by suitable mechanical connections 75, and a voltage is derived at contact 70 representing an amount of wing ice as determined by the instructor. The card 69 is energized as sh-own in the drawing at opposite ends by the A. C. voltages E and 2E respectively, and a position for slider contact 70 at the one end of the card resulting in a derived voltage 'of -2E corresponds to a condition of no ice, whereas a position for the slider contact 70 at the other end of the card resulting in a derived voltage of -E corresponds to a condition of maximum ice. The potentiometer cards 65 and 66 of the angle of attack servo (a) include the slider contacts 76 and 77 respectivel'y which are moved along the card according to the operation of the angle of attack servo, voltages being derived at the slider contacts for use in the determination of the coefficient of lift voltage CL.

In order to take into account the position of the aircraft llaps in the derivation of the coefficient of lift volt. age CL potentiometers 78 and 79 having slider contacts 80 and 81 respectively positionable through mechanical connections 82 by a student pilots flap control vdial 83 are provided. Potentiometers 78 and 79 are energized at corresponding ends as shown by the derived voltages at slider contacts 63 and 76 which respectively connect with the potentiometer cards 78 and 79 over lines 84 and 85. The other ends of cards 78 and 79 are connected to ground. A voltage is derived at each of sl'ider contacts 80and 81v according to the flap angle designated in the drawing as (Sfw) which angle is determined by the student pilot. A position for the slider contacts 80 and 81 at the grounded ends of potentiometers 78 and 79 corresponds to a ap angle of 0, Whereas a position for the slider contacts farther up valong the cards corresponds to a greater angle.

The slider contacts 64, 77, 80 and 81 of potentiometers S6, 66, 78 and 79 respectively which have been referred to hereinbefore connect with amplifier 86 providing input signals thereto. Slider contact 64 connects with amplifier 86 over line 87 to provide the input signal -CL (TC a) which is a function of thrust coefficient T C and the angle of attack a. The slider contact 77 connects over line 88 with amplifier 86 providing input signal -CL (WI, a) which signal is a function of wing ice as predetermined by the instructor and the angle a. Slider contact 80 connects over line 89 with amplifier 86 to provide input signal -CL (TC, a, Sfw), such signal being a function of the thrust coeicient TC, angle a, and the ilap angle SIW. Slider contact 81 connects with amplifier 86 over line 9i) to provide the input signal -CL (a, Sfw) which is a function of the angle of attack a and the iiap angle Sfw. The various potentiometer cards referred to as entering into the derivation of the coeicient of lift Voltage CL are all contoured so that the input signals to the amplifier 86 represent in summation the coeicient of lift voltage connection 94 and line 95 to one end of a potentiometercard 96 of the (V12) servo 45. Potentiometer 96 has its other end connected to ground. Potentiometer 96 in'-l cludes a slider contact 97 which is moved along the potentiometer card according to the operation of the (V12) servo for deriving a voltage representing lift. Such derived voltage at contact 97 is'fed over line 98 to the slider contact 28 of the potentiometer 30. The poten` tiorneter 30 is a dividing potentiometer having its slider contact 28 positioned according to the setting of the aircraft loading dial 18', and the potentiometer has an output voltage depending upon the position of the slider contact 28 which output voltage is fed over lines 99 and 100 to the amplifier 102 to provide an input signal for the amplifier representing lift divided by the mass of the aircraft.

In addition to the input signal other input signals, namely -cos 0 cos where b'designates angle of roll, and -sin 0 sin a which are derived by 1.7 t I means-of apparatus shown in Fig. 3 Aare provided foramplier y102. 1Asshown the pitch servo (0) includes .potentiornetercardl 103 :which -is contouredto provide forpthe derivation of voltages -l-.sin v},cos 0, -sin 0, and -i-cos at the yslider contacts 104,` V10i/arid 106,: and V107 respectively-which are positioned along the card according to fthe a operation `of `the pitch servo. Potentiometer card 103 is energizediat oppositefsends byY the- A. C. voltage -I-E and at themid-point byithe'A. C.ivoltage -E. The card is connected to ground .mid-way. between the center ofthe vcard and opposite: ends. `Slider contact 104 is operated along theiportionfof'thecard extending between points energized 1by thefvoltages -+Eyand Y-E respectively,.such;portion of-:thegcard being wound cosinusoidally to provide, for.:thef derivation of `the voltage -l-sin 0 at c0utact104. i Contact-105:;is operated over that portion of the, `card extendingbetweemthegrounded points, and this-portion Jis Wound sinusoidallyrto provide for the derivationj ofthe-voltage A-f-cos 0, at contact -105. The

.contact ljifunctions over al cosinusoidally wound portion of-theycardgextending betweenvthe points energized bygthey voltages +B and E to'etectthe derivation of the voltage #sin 0,nand contact 107 t functions over a sinusoidally wound portion ofthe card betweenppoints connectedftofground and the voltage-+B thereby pro viding for they derivation of the voltage +cos 0.

jSlider: contact I104 connectskover line Y108 and through resistor 109 -with one end of a potentiometer 110 included in the angle of attack (a) servo, and slider contact 106 connects overline lllto-'fthe otherfend of thepotentiometer 110. The potentiometer card connects with groundeatran intermediate point. The potentiometer includes slider contact 112 which is moved along the card in accordance with the operation of the angle of attack (a),v servo..tolprovides.anoutput'voltage sin 6 sin a at contact 112 which voltage is yfed over line 113 as an input signal to the amplifier 102. Slider contact 105 connects overv line -114-xwith-the mid-point of .the potentiometer card 115 of the angle of roll servo p) V'designated by the reference character 116 and controlledin the manner set forth in the aforementioned Patent No. 2,687,580. Slider Contact 107 connects over line 116 withppposite ends of. the potentiometer card 115, which card-is grounded mid-way between the points connected to slider Contact 105 and -107 respectively. The potentiometer 'card.115, includes slider Vcontact 117 which is operated along the card according to the operationof the angle ofroll servo (o) to provide for the derivation of a voltage at slider contact 117 which is fed to the amplier 102 as input signalcos 0 cos e. The potentiometer card 115 is sinusoidally wound.

The input signals -vcosr 0 vcos- 25, and -sin 0 sin oc -to amplifier 102 are summed therein to provide a voltage where W designates the weight of the aircraft, L is the lift, and m is the aircraft mass. As shown amplifier 102 connects with the primary winding 11S of a transformer 1 19 ,having a :secondary winding A120 providing koutput voltage at its positive output terminal which connects over the line 121 (Fig. l) with the 'slider contact 13 of the true air speedTV't) `potentiometer '5. Slidercontact- 13 is moved and a AvoltagefV't.representing truevairzspeed. The poten? tiometenS ',is'returned. to,ground from va point near its one end through the resistor y122 4and the output voltage of lthe potentiometerfis ltapped olat such point and fed over Iline 123.- to uprovide =the input signal DW-2L i to the angle of attack' vservoV (a'). In addition to'y the input signal the angle of attack servo (a) is provided with another input signal wy-by reason of the Aconnectionfof the servo amplier- 32- over lines v1.24 and'- S18-with the slider 'contact 37,0fthe (wyyfservo ,potentiometer 36. The only 'other input signal toi'the -angle ofI 'attack servo is vthe feed-.back signal efb. v The angle'of attack servo lwhichris an integrat ing servo is operated to a position representative of -the angle of attack -fandfin'accordancefwith such operation slider contact? '.125 yis-moved''alongrcosinusoidally @wound card 126 which" asshown 4connects at oneendwith=the A. C.. voltage#Brand-:connects at the other endithrough a resistor 127 .f-withthe -1A.l C. voltage 'l-E, the .potentiometer: cardnbeingrgrounded 'at an intermediate point. A t Voltage yis .thereby iderived at'y contact 125 which :is .fed over lines 128 :and 129 :tosprovidexthe input signalv-gisinu for the Vt .servoy amplifier? A2.

The rinput signal sie' representing'. the effect kof .thrust on true air Aspeed and the l signals .-i-g sin 0 and -g sin a representing theelect of gravity on `true air speedfall having been considered, the derivation of'the input signal tothe true vair speed servo will now be. presented. As hereinbefore indicated, the input signal Dp ifa represents'the `eiect of vparasitic dragon true air speed. In the computation-of lthe parasitic drag item, the 4factors ofside-'slip rudder angle (Sr), Wing ice (WI), and flap angle (Sfw) are taken into account. As shown in Fig. 4 aside-slip servo bearing the reference character 130 includes a potentiometer 131 having a slider contact 132 which is moved along the potentiometer card according to the operation of the servo. The potentiometer card is energized at opposite ends by the A. C. voltage -'|E and is connected to ground at intermediate points as illustrated. By reason of the movement of slider contact 132 along potentiometer card 131 a voltage is Vderived at the slider contact which is fed over line 133 to provide an input signal CDDQS) to summing amplier 134. The side-slip servo may be controlled as shown in the aforementioned Patent No. 2,6875 80. In addition toinput -CDD() which is al function ofthe side-slip, other input signals are provided for' the amplierrincluding input signal -Dp(Sr) which is a function Aof rudder angle.

Rudder angle is dependent upon the position of the rudder pedal 135 which is connected as shown by suitable mechanical connections 136 to a slider contact 137 of potentiometer 138. The potentiometer 138 connects at one end to the negative A. C. voltage ,-E and connects at its other end to such A. C. voltage -E through the resistor 139. The potentiometer is connected to ground at spaced intermediate points. Movement of the rudder pedal 135 to a position corresponding to a selected rudder angle (Sr) operates slider contact 137l such that a voltage is derived at the slider contact representative of the rudder angle which voltage is fed over line 140 to provide input signal -CD(Sr) Two additional signals are provided as inputs to the summing amplifier 134, namely input signal -CDD(WI,a) which is a function of wing ice and angle of attack, and input signal -CDD(Sfw) which is a function of flap angle. Input signal -CDD(W[, is computed according to the setting of instructors wing ice control dial 74 and the operation of the angle of attack servo (a). The instructors Wing ice control dial is connected by suitable mechanical means 141 with slider contact 142 of potentiometer 143, the potentiometer being energized at opposite ends by A. C. voltages E and 2E respectively. The slider contact 142 is positioned along the potentiometer card by the dial 74 and a voltage is derived at the contact which represents a particular Weight of ice on the aircraft wing. A position for slider contact 142 at one end of potentiometer card 143 which connects with .the energizing voltage -2E corresponds to a condition of maximum ice whereas a position for the slider contact at the other end of the potentiometer card corresponds to a condition of no ice. The voltage derived at slider contact 142 is fed over line 144 to both ends of a potentiometer card 145 which is included in the angle of attack (a) servo system. Potentiometer card 145 is returned to ground through a resistor 145 at a point intermediate its ends and has a slider contact 146 which is positioned along the card according to the operation of the angle of attack (a) servo, a voltage being derived at the slider contact which is fed over line 147 to amplifier 134 providing the input signal -CDD(WI, a). The input signal -CDD(S,w) is dependent upon the position of the flap control dial 83. Such dial is positioned by a student pilot according to a selected flap angle Sfw. The dial connects by suitable mechanical connections 148 with slider contact 149 of a potentiometer 150 so that the slider contact is correspondingly positioned along the potentiometer card. As shown the potentiometer card 150 is energized at one end by the negative A. C. voltage E whereas the other end is connected to ground. A voltage is derived at the slider contact 149 according to the setting of the dial 83 as determined by a student pilot, and such voltage is fed over line 150 to provide input signal -CDD(SW) for summing amplifier 134.

The various potentiometer cards entering into the derivation of the input signals -CDD(), -CDD(S,), CD(WI, a), and -CDD(S,W) for summing amplifier 134 are contoured so that such signals in summation represent the coefficient of parasitic drag CDD for varying conditions of flight. Amplifier 134 wherein the aforementioned signals are summed connects to the primary 135 of a transformer 136' having a secondary winding 137 which provides output voltage -l-CD representing the coecient of parasitic drag at its positive output terminal.

The voltage -i-CDD is fed to one end of potentiometer 200 in the (V12) servo system, potentiometer 200 having its other end connected to ground. The potentiometer includes slider contact 151 which is moved along the potentiometer card according to the operation of the (V12) servo for deriving a voltage representing parasitic drag. Such derived voltage is fed over line 152 to the slider contact 27 of the potentiometer 29 which is a dividing potentiometer having its slider contact 27 positioned according to the setting of aircraft loading dial 18'.y The l0 potentiometer has an output voltage which is fed over line 153 to the amplifier 2 to provide the input signal for the amplifier representing parasitic drag divided by aircraft mass.

As has been hereinbefore indicated, parasitic and induced drag items affecting air speed are in accordance with our invention separately computed as input signals D D,- -lm aud-t;

respectively to the (Vt) servo amplifier 2. As stated, the factors of side-slip rudder angle (Sr), wing ice (WI), and flap angle (Sfw) are taken into account in the derivation of the parasitic drag item the weight of the airplane, CL is the coefficient of lift, e is the commonly used span-efficiency factor and g being the acceleration of gravity, S the projected wing areaand b the wing span.

The quantity n, termed normal acceleration included in the above formula for is computed in a positioning servo (n) designated by reference character 154. The normal acceleration servo (n)v includes servo amplier 155 having an input line 156 which connects with lines 99 and 100 whereby amplifier 155 is provided with input signal L ifa which determines normal acceleration. The only other input signals to amplifier 155 are the feed-back and answer signal efb and -n respectively so that the servo is caused to operate to a position representative of normal acceleration. -As shown, answer signal -n is derived at slider contact157 which is positioned along the potentiometer card 158 according to the operation of the servo, the potentiometer card 158 being energized at opposite ends by the A. C. voltages -i-E and -E respectively and being connected to ground at its mid-point. The normal yis grounded at its mid-point.

`contact 162` representing the product nCLI of normal acceleration and coecient of lift which voltage except for I 1 'thewconstantK i vand the :term e which .fmaybe'htakenr fas aarconstant in. the:.aforementioned1 formula: represents fthe parasitic drag item The voltage at slider contact 156 is fed overf-line163"fto servo amplifier. 2 of' the: (-Vt):.servo;. and fthei constants are takenzinto; account .bymeans voft afsuitablyselected" input .resistor i to c provide amplifierV 2:1with i input signal which are derived in the manner setfoutrin thespecilcation according to the operation of various simulated air craft controls and the positions of instructors controls cause the (Vt) servo to be operated to a position which is representative of` true air speed. ,"Inaccordance with the operation of the (Vt) servo, slider contact 15 of potentiometer 7 is positioned :along the potentiometer card 7 which is energized at one end by the A. C. voltage .E and is connected at its otherA end to ground. A voltage isderived atits'slider contact 15, such voltage'being determined accordingto ycomputed true air speed. The slider contact15 connects over line 164 and resistor 165 to amplifier 166 which amplifier connects with the primary 167 of a transformer 168 having a secondary winding 169 providing output voltages -i-Vt and -Vt at its positive and ynegative terminals respectively, such.- output voltages representing true air speed.

. The `voltage -l-Vt representingtrueairxspeedfis utilized to. operate a simulated air speed indicator.170,means however, being provided to take altitude into account since air speed indicators do not register true air speed, but rather true air speed less an amount due to the eifect offaltitude on the operation of thezinstrument. #Such means includes altitude'servo ('h) bearing the reference character 171. The altitude servo (h) includes^aservo amplifier 172 having input signals Input signal l' V t is derived as the output voltage of potentiometer 6 vvhich is adividing potentiometer having a ground connection through resistor 173 nearV one end. The slider contact 14 'of potentiometer 6 is connected over line 174 with the winding 175 of the altitudeservo generator so. that the voltage at the slider contact represents as a .negative quantity rate of change of altitude, i. e. -IL This signal from the servo generator is' by reason of themovement of slider contact 14 along potentiometer card`6mo`dified to provide the output. signal ,of Athe potentiometer which is'fed over .line 176 to the amplifier as .feed-backsignal altitudefservoh) Avwhich f is anintegrating servo-is" caused Thepotentiometer 126 of the angle oir-attack;,servol-,(u) has its'slider contact 125 connectedyoverzline 128 and linef177to amplifier 172 to provide inputsignalx f1-sine, and potentiometer'42 of the pitch iservo.(0)':has lits'slider conta'ctfll; connected over lines 43fand" 178 tothe 'altitude to'operatef-according tothe input-signals toa position which=eis-representative of'aircraftaltitude.

As shown,l1the#altitudeeservo' includes potentiometer card '1f79-lwhichc'onnects atonecend through 'resistor 180 towgrou-rdearid Ico-nnectsat itsothet-` end loverline `181 withthe positiveioutputterminalof secondary Winding 169i having '+V g-asthe output voltage. )Thepotentiometen1t79fincldes'slider contact1182- which is 'moved along the 'potentiometer card 179 in accordance With the operation=ofrthe altitude'servo to-derive'a voltage'whiclr' is determinative of indicated air speed. Slider contact 182 .connects :with: .thef airs; speed :meter 17 0,1 fwhich may.` be a'wo'ltmeterrthrough awrectiier. 183, .the air...speedmeter being. properly vcalibratedf to register indicated; air ispeed infaccordancey with :the derived "voltage 'at slider 'contact 182.

lThetderivedvoltage :at slider contact 182 oftheA altitude potentiometer179 provideswfor'the operation ofthe V12 servo45 ywhich! has -been hereinbefore v referred toi in connectionwith`.thederivationof thezitems of parasitic-and induced f .drag

respectively;andi'thefgravitylcomponent -g sin a. I Slider Contact?13k-connects@over line..184` with the servo arnplifier f185rfofs the -"'(Vi.2) servo :to provide the inputvsignal '+V1f1representing. :indicated yair.4 speed. The other input signalsrlto :amplifierA 185 :are the feed-back 1 signal en, fromothefservo .1generator,-and'the answer signal-244V, derivedatslider contact 186v `of lthe square root 'contoured potentiometer 187,'rthepotentiometer being Yconnected-Lat onerenditothe AIT C. :voltage A "EV and being connected at .its rfother fend i'to ground. As f shown, the answer signal :.isfedifrom the slider contact 186 toamplier1185 overthe linef189. Accordingly,1 the (V12) servoiwhich is:-an.fan`sWer1servowith generator feed-back is operated tora-position.representing indicated air speed squared-V12. It should be-understood that this invention is not limited tolspecic details: of construction and arrangement thereof herein illustrated,.and that changes and modifications'may occur'ftovoneskilled inthe art Without departingrfrom the fspirit of the invention.

" iWhat is` claimed is:

1 "In aircraft=training apparatus having ight computing means adapted to compute air speed, anglefof attack, and'sideslip according to the operation of simulatedY flight controls `including a rudder control and a ap control, a-lsystemv for'y deriving. a--signal representing the eect 'of parasitic dragon air `speed, comprising means for computinglcoefcient-ofzparasiticfdrag-as a function of sideslip, rudder angle, angle of attack, and ap'angleymeans for computingwindicated air speed squared,means -for computing aircraftY mass, and means for deriving a signal representinglthe 'effectfof parasiticdrag on air speed according-to' the computed values of coeicient of parasitic draggindicatedfair speedsquared and aircraft mass.

2.'-In an Vaircraft trainer having a plurality of -controls operable by astudent pilot'including a wing flap control, function generating means-associated vwith each `of said controls for `deriving an-electricalsignal 'in accordance f With'the'position-of the. associated control, a pluralityf'of computing `systems respectivelyV lproducing output signals representing computed --aerodynamicfactors' determinative of't'hesimulated flight responsive to Vinput` signals theretoderived'ffromothers of said computing systems and from-fs'aidfunction'generatingmeans includingrl an angle Tof attack computing systemvand a thrust coefficient computing system: the improvement of provision of: a further; computing systemV .for accurately` computing .coeicientof `lift.of the l:simulated iiight for .utilization of anfoutput signalfthereof representative .of computed'co 13 ef'iicient of lift as an input signal to another of said systems, comprising electrical signal combining means delivering said computed coeicient of lift output signal, means to apply to the input side of said combining means a signal derived from the wing iap function generating means, means to apply to the input side of said combining means a signal representative of said computed angle of attack, and means to apply to the input side of said References Cited in the file of this patent UNITED STATES PATENTS Kittredge July 11, 1950 Davis et a1. Feb. 5, 1952 Fogarty et al. Apr. 28, 1953 

